1. Field of the Invention
The present invention relates to a vertical alignment active matrix liquid crystal display device using a thin film transistor (hereinafter referred to as TFT) as an active element.
2. Description of the Related Art
A vertical alignment liquid crystal display device comprises a pair of substrates opposite to each other with a predetermined gap therebetween, a plurality of pixel electrodes arranged in a matrix of rows and columns on the inner surface of one substrate of the opposing inner surfaces of the pair of substrate, a plurality of TFTs arranged on the inner surface of the one substrate correspondingly to the plurality of pixel electrodes and connected to the corresponding pixel electrodes, a plurality of gate lines and data lines formed on the inner surface of the one substrate respectively between the rows of pixel electrodes and the columns of pixel electrodes for supplying a gate signal and a data signal to the TFTs on the corresponding rows and columns, an opposing electrode formed on the inner surface of the other substrate so as to oppose to each of the plurality of pixel electrodes, vertical alignment films formed so as to cover the electrodes on the inner surfaces of the front substrate and back substrate respectively, and a liquid crystal layer having a negative dielectric anisotropy filled in the gap between the front substrate and the back substrate.
The vertical alignment liquid crystal display device displays an image by aligning liquid crystal molecules being in the vertically aligned state to lie down by applying a voltage between each of the pixel electrodes and the opposing electrode, in each of a plurality of pixels that are defined in the areas where the plurality of pixel electrodes and the opposing electrode face each other. As the voltage is applied, the liquid crystal molecules in each pixel are so aligned as to lie down to the substrate.
Such a vertical alignment liquid crystal display device causes variation in the state of lying alignment of the liquid crystal molecules in accordance with the voltages applied to the respective pixels, resulting in display unevenness.
Hence, in order to stabilize the alignment state of each pixel and obtain a wider view angle characteristic, it is proposed to form a plurality of domains where the liquid crystal molecules are aligned along plural directions pixel by pixel. For instance, as described in the specification of Japanese Patent Publication No. 2565639, a liquid crystal display apparatus proposed has the opposing electrode formed with a slit with the shape of a letter X, so that the liquid crystal molecules in each pixel are so aligned as to tilt toward the center of the X-shaped slit along the four directions when a voltage is applied between the two electrodes facing each other.
However, since it is required in this liquid crystal display device that the domains be formed which has different alignment directions from each other due to the X-shaped slit formed in each pixel, the X-shaped slit needs to be formed to have a sufficiently large width in order to prohibit the interaction between the domains. This increases the area of the slit, which is not controllable by electric fields, in each pixel, thereby reduces the area where the opposing electrode and the pixel electrode face each other, resulting in a low aperture ratio.